Methods and systems for photoacoustic monitoring using hypertonic and isotonic indicator dilutions

Abstract

A patient monitoring system may provide photoacoustic sensing based on an indicator dilution to determine one or more physiological parameters of a subject. The system may detect an acoustic pressure signal, which may include one or more thermo-dilution responses, one or more hemo-dilution responses, or a combination thereof. For example, a thermo-dilution indicator and/or a hemo-dilution indicator may be used to determine one or more hemodynamic parameters. In a further example, an isotonic indicator and a hypertonic indicator may be used to determine one or more hemodynamic parameters of the subject.

What is claimed is: 
     
       1. A system for determining a value of the physiological parameter of a subject, the system comprising:
 a light source configured to provide a photonic signal to a first blood vessel site of the subject; 
 an acoustic detector configured to detect an acoustic pressure signal from the first blood vessel site, wherein the acoustic pressure signal is caused by absorption of at least some of the photonic signal by one or more constituents at the first blood vessel site, and wherein the acoustic pressure signal comprises:
 a first acoustic pressure response based on an isotonic indicator provided to a second blood vessel site at a first time, and 
 a second acoustic pressure response based on a hypertonic indicator provided to the second blood vessel site at a second time, wherein the first time and the second time are during the same clinical session; and 
 
 processing equipment configured to determine a value of the physiological parameter of the subject based on the first response and the second response. 
 
     
     
       2. The system of  claim 1 , wherein the second blood vessel site comprises a site of a vein of the subject. 
     
     
       3. The system of  claim 1 , wherein the first blood vessel site comprises a site of a pulmonary artery of the subject. 
     
     
       4. The system of  claim 1 , wherein the first blood vessel site comprises a site of the aorta of the subject. 
     
     
       5. The system of  claim 1 , wherein the physiological parameter comprises cardiac output. 
     
     
       6. The system of  claim 1 , wherein the physiological parameter comprises extravascular lung water. 
     
     
       7. The system of  claim 1 , wherein the isotonic indicator comprises a saline solution having a concentration of about nine grams of sodium per liter of water. 
     
     
       8. The system of  claim 1 , wherein the hypertonic indicator comprises a saline solution having a concentration of about fifty grams of sodium per liter of water. 
     
     
       9. The system of  claim 1 , wherein at least one of the isotonic indicator and the hypertonic indicator comprises a dye indicator. 
     
     
       10. The system of  claim 1 , wherein the processing equipment is further configured to:
 generate a dilution curve based at least in part on at least one of the first response and the second response; and 
 determine the physiological parameter of the subject further based at least in part on a time integral of the dilution curve. 
 
     
     
       11. The system of  claim 1 , wherein the physiological parameter comprises a pulse rate, a blood pressure, an arterial blood oxygen saturation, a venous blood oxygen saturation, an oxygenated hemoglobin concentration, a deoxygenated hemoglobin concentration, or any combination thereof. 
     
     
       12. A system for determining a value of a physiological parameter of a subject, the system comprising:
 a light source configured to provide a photonic signal to a site of a pulmonary artery or an aorta of a subject; 
 one or more acoustic detectors configured to detect an acoustic pressure signal from the site of the pulmonary artery or the aorta of the subject, wherein the acoustic pressure signal is caused by the absorption of a portion of the photonic signal by the pulmonary artery or the aorta, and wherein the acoustic pressure signal comprises:
 a first acoustic pressure response based on an isotonic indicator provided to a site of a vein of the subject at a first time, and 
 a second acoustic pressure response based on a hypertonic indicator provided to the site of the vein of the subject at a second time, wherein the first time and the second time are during the same clinical session; and 
 
 processing equipment configured to determine a value of the physiological parameter of the subject based on the first response and the second response. 
 
     
     
       13. The system of  claim 12 , wherein the physiological parameter comprises cardiac output. 
     
     
       14. The system of  claim 12 , wherein the physiological parameter comprises extravascular lung water. 
     
     
       15. The system of  claim 12 , wherein the isotonic indicator comprises a saline solution having a concentration of about nine grams of sodium per liter of water. 
     
     
       16. The system of  claim 12 , wherein the hypertonic indicator comprises a saline solution having a concentration of about fifty grams of sodium per liter of water. 
     
     
       17. The system of  claim 12 , wherein at least one of the isotonic indicator and the hypertonic indicator comprises a dye indicator. 
     
     
       18. The system of  claim 12 , wherein the processing equipment is further configured to:
 generate a dilution curve based at least in part on at least one of the first response and the second response; and 
 determine the physiological parameter of the subject based at least in part on a time integral of the dilution curve. 
 
     
     
       19. The system of  claim 12 , wherein the physiological parameter comprises an intrathoracic blood volume, an intrathoracic circulatory volume, a global end-diastolic volume, a pulmonary circulatory volume, or any combination thereof. 
     
     
       20. The system of  claim 12 , wherein the physiological parameter comprises a pulse rate, a blood pressure, an arterial blood oxygen saturation, a venous blood oxygen saturation, an oxygenated hemoglobin concentration, a deoxygenated hemoglobin concentration, or any combination thereof. 
     
     
       21. The system of  claim 1 , wherein the physiological parameter comprises an intrathoracic blood volume, an intrathoracic circulatory volume, a global end-diastolic volume, a pulmonary circulatory volume, or any combination thereof.